Adipex, which contains phentermine, typically stays in your system for about 4 to 7 days after the last dose. The half-life of phentermine is approximately 20 hours, meaning it takes about 20 hours for the body to eliminate half of the drug. Complete elimination usually requires about 5 to 6 half-lives, translating to roughly 4 to 6 days

. Phentermine is primarily excreted unchanged in the urine (62-85%), and its elimination can be influenced by the acidity of the urine. Acidic urine (pH < 5) can speed up elimination, reducing the half-life to 7-8 hours, while more alkaline urine slows it down

. In terms of detection:

• Phentermine can be detected in urine for about 2 to 6 days after the last dose, with 4 days being typical

• It can be detected in oral swabs for about 48 hours

• Hair follicle tests can detect phentermine for up to 90 days

Because phentermine is chemically similar to amphetamines, it may cause false- positive results for amphetamines on drug tests, even if amphetamines are not present

. In summary, Adipex (phentermine) generally remains in your system and detectable in urine for about 4 to 7 days, but this can vary based on individual metabolism, kidney function, urine pH, dosage, and duration of use.